Exception Code 2 - StartAddress being passed as 0 about iot-edge-modbus HOT 4 CLOSED

Hi,

For read operation, address "40001" means a read holding registers at address 1 (https://en.wikipedia.org/wiki/Modbus#Coil.2C_discrete_input.2C_input_register.2C_holding_register_numbers_and_addresses). When convert to PDU data frame, it becomes function code of 3, and starting address as 0. So the StartingAddress shown in the request from Modbus module to your Modbus target is 0 (in PDU format).

Please do double check your configuration and the Modbus device user manual to see if there's holding registers available at address 1.

Could you capture the logs which containing the exception messages? And your module configuration details. Thanks!

from iot-edge-modbus.

Hi, thanks for the reply.
I've not done anything with Modbus before so apologies in advance. From what I understand, 40001 contains data, Uint32.

40001 | 40002 | 2 | R | 0x03 | SID | Well-known value....

I've used a tool, modpol.exe to request data starting at the same register and it returned data, 5 registers.

modpoll.exe -c 5 -r 40001 -m tcp 192.168.x.x
modpoll 3.6 - FieldTalk(tm) Modbus(R) Master Simulator
Copyright (c) 2002-2018 proconX Pty Ltd
Visit https://www.modbusdriver.com for Modbus libraries and tools.

Protocol configuration: MODBUS/TCP
Slave configuration...: address = 1, start reference = 40001, count = 5
Communication.........: 192.168.x.x, port 502, t/o 1.00 s, poll rate 1000 ms
Data type.............: 16-bit register, output (holding) register table

-- Polling slave... (Ctrl-C to stop)
[40001]: 21365
[40002]: 28243
[40003]: 1
[40004]: 65
[40005]: 18034

I changed the register to 40098, float, still have the same problem.
Below is the config of the modbus module, pretty much the same as the example except for the IP and the register.

{
  "properties.desired": {
    "PublishInterval": "60000",
    "SlaveConfigs": {
      "Slave01": {
        "SlaveConnection": "192.168.x.x",
        "HwId": "PowerMeter-0a:01:01:01:01:01",
        "Operations": {
          "Op01": {
            "PollingInterval": "30000",
            "UnitId": "1",
            "StartAddress": "40001",
            "Count": "2",
            "DisplayName": "Voltage"
          }
        }
      }
    }
  }
}

The saved properties according to the modbus module

Saving reported properties: {"PublishInterval":60000,"SlaveConfigs":{"Slave01":{"Operations":{"Op01":{"PollingInterval":30000,"UnitId":1,"StartAddress":"40001","Count":2,"DisplayName":"Voltage","CorrelationId":"DefaultCorrelationId"}},"SlaveConnection":"192.168.x.x","RetryCount":10,"RetryInterval":50,"TcpPort":502,"HwId":"PowerMeter-0a:01:01:01:01:01","BaudRate":null,"StopBits":null,"DataBits":null,"Parity":null}}}

And the exception

Modbus exception code: 2

The successful trace results from modpol.exe shows the starting register as 40000

And the unsuccessful trace results from modbus module shows the starting address as 0

Thanks again

from iot-edge-modbus.

Based on your master simulator tool "modpoll" document https://www.modbusdriver.com/modpoll.html , I think you misunderstand how to mapping "reference number" to Modbus module configuration "StartAddress".
When use "modpoll", with "-r 40000" only, which means to use default operation type of "-t 4 16-bit output (holding) register data type (default)".
The full compatible command line should be :
modpoll.exe -c 5 -r 40001 -t 4 -a 1 -m tcp 192.168.x.x
To map to the Modbus module configuration, "-a 1" maps to "UnitId": "1"; "-t 4" means to read from holding register, which is function code 3, so the StartAddress will start with digit 4; "-r 40001" means to read holding register from address 40001, and combining with the function code, the starting digit will be 4, so it maps to "StartAddress": "440001".
You should configure Modbus module like this for your test case:

"Op01": {
"PollingInterval": "30000",
"UnitId": "1",
"StartAddress": "440001",
"Count": "2",
"DisplayName": "Voltage"
}

from iot-edge-modbus.

Thanks, that sorted it. Appreciate your help!

from iot-edge-modbus.